Method for producing particles comprising polyhydroxyalkanoates and particles produced thereby

Abstract

The present invention relates to a method for producing granules comprising a polyhydroxyalkanoate, and granules produced thereby, the method comprising: (1) a step of injecting a raw material comprising a polyhydroxyalkanoate (PHA) and an additive into a twin-screw extruder to form a polyhydroxyalkanoate melt; (2) a step of supplying a polyhydroxyalkanoate melt to a template by means of a gear pump; (3) a step of passing the polyhydroxyalkanoate melt through a template to form a polyhydroxyalkanoate melt line; and (4) a step of cutting and crystallizing the polyhydroxyalkanoate melt wire in an underwater pelletizer to form pellets.

Description

Technical Field

[0001] The present disclosure relates to a method for preparing particles containing polyhydroxyalkanoate having a controlled molecular weight, and to an apparatus for preparing the particles. Background Art

[0002] Generally, synthetic resins are widely used in the manufacture of various products due to their excellent physical properties, low price, and light weight. However, synthetic resins have a major problem in that they do not decompose well; thus, they are a major cause of environmental pollution. Therefore, in recent years, environmentally friendly and renewable plant-derived biodegradable resins have attracted attention.

[0003] Polyhydroxyalkanoate (one of the above biodegradable resins) has physical properties similar to those of general synthetic resins (such as polyethylene or polypropylene), while having the advantage of being able to be naturally decomposed by microorganisms in soil or the ocean; thus, attempts are being made to use it to manufacture various products.

[0004] An example of a method for manufacturing a product from polyhydroxyalkanoate is the steps of producing polyhydroxyalkanoate, granulating it, and then molding it. Specifically, polyhydroxyalkanoate is produced by culturing microorganisms, crushing the microorganisms, and then purifying with an organic solvent and / or water to recover polyhydroxyalkanoate as a resin component. Subsequently, the recovered polyhydroxyalkanoate can be extruded through an extruder or the like, granulated by cutting or the like, and then molded to manufacture a product.

[0005] However, since crystalline or semi-crystalline polyhydroxyalkanoate is sensitive to heat, when subjected to high temperature and the pressure of high-speed rotation and friction of a screw during the extrusion process, there is a problem that the molecular weight of the granulated polyhydroxyalkanoate rapidly decreases. The decrease in molecular weight impairs mechanical properties (such as elongation and impact strength), which limits the ability to ensure the physical properties of the final product.

[0006] [Prior Art Documents]

[0007] [Patent Documents]

[0008] (Patent Document 1) Korean Patent No. 10-1485386 Summary of the Invention

[0009] Technical Problem

[0010] In order to solve the above conventional problems, an object of the present disclosure is to provide a method for preparing particles, which can control the decrease in the molecular weight of polyhydroxyalkanoate during the process of preparing particles from a raw material containing polyhydroxyalkanoate.

[0011] In addition, another object of the present disclosure is to provide particles prepared by the above preparation method.

[0012] In addition, another object of the present disclosure is to provide an apparatus for preparing particles, which can prepare particles while controlling the reduction of the molecular weight of polyhydroxyalkanoates.

[0013] Technical Solution

[0014] To achieve the above object, the present disclosure provides a method for preparing particles, which includes: (1) feeding a raw material containing polyhydroxyalkanoate (PHA) and an additive into a twin-screw extruder to form a polyhydroxyalkanoate melt; (2) supplying the polyhydroxyalkanoate melt to a die plate through a gear pump; (3) passing the polyhydroxyalkanoate melt through the die plate to form a polyhydroxyalkanoate melt strand; and (4) cutting and crystallizing the polyhydroxyalkanoate melt strand in an underwater pelletizer to form particles.

[0015] According to an embodiment of the present disclosure, in step (1), the barrel temperature of the twin-screw extruder can be 120 to 160 °C.

[0016] According to another embodiment of the present disclosure, in step (1), the temperature of the polyhydroxyalkanoate melt can be 130 to 160 °C.

[0017] According to another embodiment of the present disclosure, in step (1), the additive can include at least one of a slip agent and a nucleating agent.

[0018] According to another embodiment of the present disclosure, the amount of the additive can be 0.1 to 20 parts by weight relative to 100 parts by weight of the polyhydroxyalkanoate.

[0019] According to another embodiment of the present disclosure, in step (1), the polyhydroxyalkanoate can be a crystalline polyhydroxyalkanoate, a semi-crystalline polyhydroxyalkanoate, or an amorphous polyhydroxyalkanoate.

[0020] According to another embodiment of the present disclosure, in step (1), the polyhydroxyalkanoate can be a copolymer containing repeating units derived from at least one selected from the group consisting of: 3-hydroxybutyrate (3-HB), 3-hydroxypropionate (3-HP), 3-hydroxyvalerate (3-HV), 3-hydroxyhexanoate (3-HH), 4-hydroxybutyrate (4-HB), 4-hydroxyvalerate (4-HV), 4-hydroxyhexanoate (4-HH), 5-hydroxyvalerate (5-HV), and 6-hydroxyhexanoate (6-HH).

[0021] According to another embodiment of the present disclosure, the polyhydroxyalkanoate can be a copolymer containing repeating units derived from 4-hydroxybutyrate (4-HB), and the amount of the repeating units is 1 to 60% by weight based on the total weight of the copolymer.

[0022] According to another embodiment of the present disclosure, the polyhydroxyalkanoate may be poly(3-hydroxybutyrate-co-4-hydroxybutyrate).

[0023] According to another embodiment of the present disclosure, in step (2), the pressure difference of the gear pump before and after the polyhydroxyalkanoate melt passes through may be 60 to 180 bar.

[0024] According to another embodiment of the present disclosure, in step (3), the temperature of the template may be 120 to 190°C.

[0025] According to another embodiment of the present disclosure, in step (4), the temperature of the circulating water bath equipped in the underwater pelletizer may be 40 to 80°C.

[0026] According to another embodiment of the present disclosure, the method for preparing particles may further include (5) dehydrating and drying the particles formed in step (4).

[0027] According to another embodiment of the present disclosure, the molecular weight reduction rate (M) of the polyhydroxyalkanoate according to the following equation 1 is: d ) can be 15% or lower.

[0028] [Equation 1]

[0029] M d ={(M1-M2) / M1}×100

[0030] In Equation 1, M1 is the weight average molecular weight of the polyhydroxyalkanoate contained in the raw material, and M2 is the weight average molecular weight of the polyhydroxyalkanoate contained in the particles.

[0031] Meanwhile, in order to achieve the above objectives, the present disclosure provides particles prepared by the above preparation method.

[0032] In addition, in order to achieve the above-mentioned purpose, the present disclosure provides an apparatus for preparing particles, which includes a twin-screw extruder, which is used to form a polyhydroxyalkanoate melt from a raw material containing polyhydroxyalkanoate (PHA) and an additive; a gear pump, which is arranged at the rear end of the twin-screw extruder, for conveying the polyhydroxyalkanoate melt; a die plate, which is used to form a polyhydroxyalkanoate melt line from the polyhydroxyalkanoate melt conveyed by the gear pump; and an underwater pelletizer, which is used to cut and crystallize the polyhydroxyalkanoate melt line formed by the die plate to form particles.

[0033] Beneficial effects of the present invention

[0034] In the present disclosure, a raw material containing polyhydroxyalkanoate is processed in a twin-screw extruder in a low-temperature and low-pressure environment to obtain a polyhydroxyalkanoate melt, and then the polyhydroxyalkanoate melt is conveyed by a gear pump. Therefore, the conventional problem that the molecular weight of polyhydroxyalkanoate rapidly decreases during the granulation process due to the stress caused by the high-temperature and high-pressure environment of the twin-screw extruder can be solved. In addition, in the present disclosure, since additives are added to the twin-screw extruder during the granulation process, the decrease in the molecular weight of polyhydroxyalkanoate can be controlled.

[0035] Therefore, the present disclosure can provide particles containing polyhydroxyalkanoate with a minimized decrease in molecular weight. When using the particles to manufacture various articles, articles having excellent physical properties (mechanical properties) (e.g., films, straws, containers, trays, cups, etc.) can be obtained. Brief Description of the Drawings

[0036] Figure 1 is a flowchart showing a method for preparing particles according to an embodiment of the present disclosure.

[0037] Figure 2 is a schematic diagram showing an apparatus for preparing particles according to an embodiment of the present disclosure. Detailed Description of the Embodiments

[0038] Hereinafter, the present disclosure will be described in detail. The present disclosure is not limited to the forms given below, but can be modified into various forms as long as the gist of the present disclosure is not changed.

[0039] In this specification, the term "comprising" is intended to specify a particular feature, region, step, process, element, and / or component. It does not exclude the presence or addition of any other feature, region, step, process, element, and / or component, unless specifically stated to the contrary.

[0040] All numbers and expressions related to the quantity of components, reaction conditions, etc. used herein should be understood to be modified by the term "about" unless otherwise specified.

[0041] For convenience of description, the dimensions of each element in the drawings may be exaggeratedly depicted and they may be different from the actual dimensions.

[0042] The present disclosure is characterized by minimizing the degree to which a raw material containing polyhydroxyalkanoate (PHA) is exposed to a high-temperature and high-pressure environment during the granulation process, thereby controlling the decrease in the molecular weight (weight-average molecular weight or number-average molecular weight) of polyhydroxyalkanoate. The present disclosure will be described in detail below.

[0043] Method for Preparing Particles

[0044] The method for preparing particles according to the present disclosure includes: (1) feeding a raw material containing polyhydroxyalkanoate (PHA) and an additive into a twin-screw extruder to form a polyhydroxyalkanoate melt; (2) supplying the polyhydroxyalkanoate melt to a die through a gear pump; (3) passing the polyhydroxyalkanoate melt through the die to form polyhydroxyalkanoate melt strands; and (4) cutting and crystallizing the polyhydroxyalkanoate melt strands in a underwater pelletizer to form particles.

[0045] Hereinafter, each step will be described with reference to Figure 1 each description.

[0046] Step (1): Formation of polyhydroxyalkanoate melt

[0047] According to the present disclosure, step (1) is a step of feeding a raw material containing polyhydroxyalkanoate (PHA) and an additive into a twin-screw extruder to form a polyhydroxyalkanoate melt.

[0048] The polyhydroxyalkanoate contained in the raw material has physical properties similar to those of synthetic biodegradable polymers derived from petroleum (such as polybutylene adipate terephthalate (PBAT), polybutylene succinate (PBS), polybutylene terephthalate succinate (PBST), and polybutylene adipate succinate (PBSA)), and has excellent properties in terms of biodegradability and biocompatibility.

[0049] The polyhydroxyalkanoate can be obtained by cell disruption using mechanical methods or physical methods, or it can be obtained by cell disruption using non-mechanical methods or chemical methods.

[0050] Specifically, the polyhydroxyalkanoate can be a copolymer containing repeating units derived from at least one (at least one monomer) selected from the group consisting of: 3-hydroxybutyrate (3-HB), 3-hydroxypropionate (3-HP), 3-hydroxyvalerate (3-HV), 3-hydroxyhexanoate (3-HH), 4-hydroxybutyrate (4-HB), 4-hydroxyvalerate (4-HV), 4-hydroxyhexanoate (4-HH), 5-hydroxyvalerate (5-HV), and 6-hydroxyhexanoate (6-HH), but is not limited thereto.

[0051] The polyhydroxyalkanoate can be crystalline polyhydroxyalkanoate (cPHA), semi-crystalline polyhydroxyalkanoate (scPHA), or amorphous polyhydroxyalkanoate (aPHA), depending on the type of monomer and the content of the repeating units derived therefrom. Specifically, the polyhydroxyalkanoate can be classified into cPHA, scPHA, or aPHA because its crystallinity is controllable depending on the content of the repeating units derived from 4-hydroxybutyrate (4-HB).

[0052] The polyhydroxyalkanoate can be a copolymer containing repeating units derived from 4-hydroxybutyrate (4-HB), and the amount thereof is 1 to 60% by weight, 1 to 55% by weight, 1 to 50% by weight, 1 to 45% by weight, 1 to 40% by weight, 1 to 35% by weight, 1 to 30% by weight, 1 to 25% by weight, 2 to 23% by weight, 3 to 20% by weight, 4 to 15% by weight, 5 to 15% by weight, 6 to 14% by weight, or 7 to 13% by weight based on the total weight of the copolymer (polyhydroxyalkanoate), but is not limited thereto.

[0053] For example, the polyhydroxyalkanoate can be poly(3-hydroxybutyrate-co-4-hydroxybutyrate). In this case, the content of the 4-HB repeating units contained in poly(3-hydroxybutyrate-co-4-hydroxybutyrate) can be 1 to 60% by weight, 1 to 55% by weight, 1 to 50% by weight, 1 to 45% by weight, 1 to 40% by weight, 1 to 35% by weight, 1 to 30% by weight, 1 to 25% by weight, 2 to 23% by weight, 3 to 20% by weight, 4 to 15% by weight, 5 to 15% by weight, 6 to 14% by weight, or 7 to 13% by weight based on the total weight of poly(3-hydroxybutyrate-co-4-hydroxybutyrate), but is not limited thereto.

[0054] When the polyhydroxyalkanoate is scPHA, the crystallization temperature (Tc) can be 50 to 120 °C, 55 to 115 °C, 65 to 105 °C, or 75 to 95 °C, but is not limited thereto. In addition, when the polyhydroxyalkanoate is scPHA, the melting temperature (Tm) can be 110 to 170 °C, 115 to 160 °C, or 120 to 150 °C, but is not limited thereto.

[0055] The weight-average molecular weight (Mw) of the polyhydroxyalkanoate can be 100,000 to 800,000 g / mol, 150,000 to 750,000 g / mol, 200,000 to 700,000 g / mol, or 250,000 to 650,000 g / mol, but is not limited thereto.

[0056] The polydispersity index (PDI) of the polyhydroxyalkanoate can be 1.0 or greater, 1.2 or greater, 1.5 or greater, 1.8 or greater, 1.9 or greater, or 2.0 or greater, and 5.0 or less, 4.0 or less, 3.0 or less, 2.9 or less, 2.8 or less, 2.7 or less, 2.6 or less, or 2.5 or less, but is not limited thereto.

[0057] In addition to polyhydroxyalkanoates, the raw materials containing polyhydroxyalkanoates may optionally contain known synthetic resins (e.g., polyethylene (PE), polypropylene (PP), or a mixture thereof) and / or biodegradable resins (e.g., polylactic acid (PLA), polyvinyl alcohol (PVOH), ethylene-vinyl alcohol copolymer (EVOH), poly(butylene adipate-co-terephthalate) (PBAT), polybutylene succinate (PBS), polycaprolactone (PCL), or a mixture thereof).

[0058] Meanwhile, in the present disclosure, even if the polyhydroxyalkanoate is a heat-sensitive cPHA or scPHA, the twin-screw extruder for processing the raw materials containing cPHA or scPHA is controlled to operate at relatively low temperature and low pressure; thus, the molecular weight of cPHA or scPHA can be prevented from rapidly decreasing due to exposure to high temperature and high pressure environment.

[0059] Specifically, when the twin-screw extruder is operating, the barrel temperature can be 120 to 160 °C, more specifically, 120 to 158 °C, 120 to 155 °C, 123 to 155 °C, 125 to 153 °C, or 125 to 150 °C, but not limited thereto. In addition, when the twin-screw extruder is operating, the screw rotation speed can be 60 to 150 rpm, specifically, 65 to 145 rpm, 70 to 140 rpm, 75 to 130 rpm, or 80 to 120 rpm, but not limited thereto. Since both the barrel temperature and the screw rotation speed of the twin-screw extruder are within the above ranges, a polyhydroxyalkanoate melt can be smoothly formed while minimizing the decrease in the molecular weight of the polyhydroxyalkanoate.

[0060] The additives contained in the raw materials have the property of increasing the fluidity of the polyhydroxyalkanoate melt. The additive includes at least one of a slip agent and a nucleating agent. When at least one of the slip agent and the nucleating agent is introduced into the twin-screw extruder, the crystallinity of the polyhydroxyalkanoate is controlled, thereby increasing the fluidity (flowability) of the polyhydroxyalkanoate melt; thus, the polyhydroxyalkanoate melt can be smoothly discharged from the twin-screw extruder.

[0061] Specifically, the slip agent can function to smoothly discharge the polyhydroxyalkanoate melt from the twin-screw extruder. In addition, the slip agent can also function to prevent the polyhydroxyalkanoate melt from sticking to the die or prevent the cut polyhydroxyalkanoate particles from sticking to each other during the granulation cutting process.

[0062] The slip agent is not particularly limited as long as it is a known slip agent that can be applied to polymer resins. Specifically, it can be at least one selected from the group consisting of amide-based substances, metal fatty acids, and wax-based substances.

[0063] The amide-based substance is not particularly limited. Specifically, it may include at least one selected from the group consisting of: ethylene bis(stearamide), oleamide, erucamide, and stearamide.

[0064] The metal fatty acid is not particularly limited. Specifically, it may include at least one selected from the group consisting of: calcium stearate, zinc stearate, magnesium stearate, aluminum stearate, potassium oleate, zinc oleate, magnesium oleate, aluminum oleate, calcium palmitate, zinc palmitate, magnesium palmitate, and aluminum palmitate.

[0065] The wax-based substance is not particularly limited. Specifically, it may include at least one selected from the group consisting of: beeswax, carnauba wax, and candelilla wax.

[0066] The nucleating agent can affect the crystallinity of polyhydroxyalkanoate during the process of converting the raw material containing polyhydroxyalkanoate into a melt, thereby improving the cooling and cutting processes of forming particles from the polyhydroxyalkanoate melt.

[0067] The nucleating agent is not particularly limited as long as it is a well-known nucleating agent that can be applied to the polymer resin. Specifically, it may include at least one selected from the group consisting of: calcium carbonate, silica, talc, boron nitride, and sorbitol derivatives.

[0068] Meanwhile, in addition to the slip agent and the nucleating agent, the additive may further include other well-known additives that can be applied to the polymer resin (biodegradable resin).

[0069] The additive can be premixed with the polyhydroxyalkanoate and then fed into the twin-screw extruder, or it can be fed separately into the twin-screw extruder from the polyhydroxyalkanoate through a separate feeder.

[0070] With respect to 100 parts by weight of the polyhydroxyalkanoate contained in the raw material, the addition amount of the additive may be 0.1 to 20 parts by weight, specifically, 0.1 to 15 parts by weight, 0.2 to 13 parts by weight, 0.2 to 10 parts by weight, 0.3 to 8 parts by weight, or 0.5 to 5 parts by weight, but not limited thereto. When the addition amount of the additive is within the above range, the fluidity of the polyhydroxyalkanoate melt and the cooling / cutting process efficiency can be significantly improved while minimizing the reduction in the molecular weight of the polyhydroxyalkanoate. For example, with respect to 100 parts by weight of the polyhydroxyalkanoate contained in the raw material, the addition amount of the lubricant may be 0.1 to 10 parts by weight, specifically, 0.2 to 8 parts by weight, 0.3 to 7 parts by weight, 0.4 to 6 parts by weight, 0.5 to 5 parts by weight, or 0.8 to 3 parts by weight, but not limited thereto. In addition, with respect to 100 parts by weight of the polyhydroxyalkanoate contained in the raw material, the addition amount of the nucleating agent may be 0.1 to 10 parts by weight, specifically, 0.2 to 8 parts by weight, 0.3 to 7 parts by weight, 0.4 to 6 parts by weight, 0.5 to 5 parts by weight, or 0.8 to 3 parts by weight, but not limited thereto.

[0071] The temperature of the polyhydroxyalkanoate melt formed by step (1) may specifically be 130 to 160 °C, more specifically, 130 to 158 °C, 133 to 155 °C, 133 to 153 °C, or 135 to 150 °C, but not limited thereto. When the temperature of the polyhydroxyalkanoate melt is within the above range, the polyhydroxyalkanoate melt can maintain a stable molten state while preventing thermal decomposition of the polyhydroxyalkanoate.

[0072] Step (2): Supply through gear pump

[0073] According to the present disclosure, step (2) is a step of supplying the polyhydroxyalkanoate melt to the die through a gear pump. By step (2), the fluidity (flowability) of the polyhydroxyalkanoate melt can be ensured, thereby improving the efficiency of preparing the particles. That is to say, if the twin-screw extruder operates at a relatively low temperature and low pressure to control the reduction in the molecular weight of the polyhydroxyalkanoate in step (1), the polyhydroxyalkanoate melt thus formed may have a high viscosity and thus poor fluidity. In the present disclosure, the polyhydroxyalkanoate melt is transported through a gear pump, thereby ensuring the fluidity of the polyhydroxyalkanoate melt and improving the overall efficiency of preparing the particles.

[0074] The operating conditions of the gear pump for supplying the polyhydroxyalkanoate melt to the die are not particularly limited. However, the pressure difference in the gear pump before and after the polyhydroxyalkanoate melt passes through the gear pump can be 60 - 180 bar. In this case, the pressure of the gear pump after the polyhydroxyalkanoate melt passes through it may be higher than that before it passes through. Specifically, the difference (P2 - P1) between the pressure of the gear pump before the polyhydroxyalkanoate melt passes through it (P1) and the pressure of the gear pump after it passes through the gear pump (P2) can be 60 to 180 bar, 60 to 175 bar, 60 to 170 bar, 65 to 165 bar, 70 to 160 bar, 75 to 150 bar, or 80 to 140 bar, but is not limited thereto. When the difference (P2 - P1) in the gear pump is within the above range, the polyhydroxyalkanoate melt can be smoothly supplied to the die while controlling the reduction of the polyhydroxyalkanoate molecular weight.

[0075] Meanwhile, the flow rate of the polyhydroxyalkanoate melt supplied by the gear pump (the flow rate of the polyhydroxyalkanoate melt supplied to the die) is not particularly limited and can be appropriately adjusted according to the scale of the twin-screw extruder.

[0076] Step (3): Formation of polyhydroxyalkanoate melt strand

[0077] According to the present disclosure, step (3) is a step of passing the polyhydroxyalkanoate melt that has been supplied to the die pump by the gear pump through the die to form a polyhydroxyalkanoate melt strand.

[0078] The temperature of the die for forming the polyhydroxyalkanoate melt strand is not particularly limited, but it can specifically be 120 to 190 °C. More specifically, the die temperature can be 123 to 188 °C, 125 to 185 °C, 128 to 185 °C, 130 to 185 °C, 133 to 182 °C, 135 to 180 °C, 138 to 178 °C, or 140 to 175 °C. When the temperature of the die is within the above range, the polyhydroxyalkanoate melt strand can be smoothly formed while controlling the reduction of the polyhydroxyalkanoate molecular weight.

[0079] Step (4): Formation of pellets

[0080] According to the present disclosure, step (4) is a step of cutting and crystallizing the polyhydroxyalkanoate melt strand in an underwater pelletizer (underwater cutting machine) to form pellets. Specifically, when the polyhydroxyalkanoate melt strand is supplied to the underwater pelletizer, it is cut into a predetermined size to form polyhydroxyalkanoate flakes, and then the polyhydroxyalkanoate flakes undergo a crystallization process through a circulating water bath equipped in the underwater pelletizer to form pellets.

[0081] The temperature of the circulating water bath provided in the underwater pelletizer is not particularly limited, but it can specifically be 40 to 80 °C. More specifically, the temperature of the circulating water bath can be 43 to 80 °C, 45 to 80 °C, 48 to 78 °C, 50 to 75 °C, 53 to 73 °C, or 55 to 70 °C, but not limited thereto. When the temperature of the circulating water bath is within the above range, the cooling and crystallization of the cut polyhydroxyalkanoate sheets can be well achieved, and thus pellets with desired physical properties can be prepared.

[0082] Meanwhile, the method for preparing pellets according to the present disclosure may further include dehydrating and drying the pellets formed in step (4) (step (5)). Specifically, a centrifugal dehydrator can be used to dehydrate the pellets to preliminarily remove the water contained in the pellets, and then the pellets can be dried at 40 to 100 °C for 1 to 24 hours to secondarily remove the water contained in the pellets.

[0083] In the present disclosure as described above, the polyhydroxyalkanoate contained in the raw material is processed in a twin-screw extruder in a low-temperature and low-pressure environment, conveyed by a gear pump, and then only exposed to a high-pressure environment before pelletization. Therefore, the reduction of the molecular weight of the polyhydroxyalkanoate can be minimized in the pelletization step.

[0084] Specifically, when the above preparation method is used in the present disclosure to prepare pellets, the molecular weight of the polyhydroxyalkanoate contained in the raw material in step (1) and the molecular weight of the polyhydroxyalkanoate contained in the pellets formed in step (4) can be at the same level. Specifically, when preparing pellets according to the present disclosure, the reduction rate (M d ) of the molecular weight of the polyhydroxyalkanoate according to the following Equation 1 can be 15% or less. More specifically, the reduction rate (M d ) of the molecular weight of the polyhydroxyalkanoate can be 14% or less, 13% or less, 12% or less, 11% or less, or 10% or less (for example, 0.05 to 15%, 0.1 to 10%, 0.1 to 5%, or 0.2 to 1%). When the reduction rate (M d ) of the molecular weight of the polyhydroxyalkanoate is 15% or less, articles (molded articles) with high mechanical properties (such as elongation and impact strength) can be provided.

[0085] [Equation 1]

[0086] M d ={(M1 - M2) / M1}×100

[0087] In Equation 1, M1 is the weight-average molecular weight of the polyhydroxyalkanoate contained in the raw material, and M2 is the weight-average molecular weight of the polyhydroxyalkanoate contained in the pellets.

[0088] Pellets

[0089] The present disclosure provides particles prepared by the above-described preparation method. When the particles according to the present disclosure are prepared by the above-described preparation method, the molecular weight of the polyhydroxyalkanoate contained in the particles can be at the same level (or a similar level) as the molecular weight of the polyhydroxyalkanoate initially used as a raw material.

[0090] When the particles according to the present disclosure contain a polyhydroxyalkanoate having a minimized molecular weight reduction as described above, they can have excellent mechanical properties such as elongation at break and impact strength. Therefore, when the particles according to the present disclosure are used to manufacture various articles, articles having excellent mechanical properties and excellent biodegradability can be manufactured.

[0091] These articles are not particularly limited, but they can specifically be films, straws, containers, trays, or cups.

[0092] Equipment for preparing particles

[0093] The present disclosure provides an apparatus for preparing the above-described particles. Specifically, the apparatus for preparing particles according to the present disclosure includes: a twin-screw extruder for forming a polyhydroxyalkanoate melt from a raw material containing a polyhydroxyalkanoate (PHA) and an additive; a gear pump provided at the rear end of the twin-screw extruder for conveying the polyhydroxyalkanoate melt; a die for forming a polyhydroxyalkanoate melt strand from the polyhydroxyalkanoate melt conveyed by the gear pump; and an underwater pelletizer for cutting and crystallizing the polyhydroxyalkanoate melt strand formed by the die to form particles. Hereinafter, this will be described with reference to Figure 2 to describe.

[0094] Twin-screw extruder (10)

[0095] The twin-screw extruder (10) equipped in the apparatus for preparing particles according to the present disclosure forms a polyhydroxyalkanoate melt from a raw material containing a polyhydroxyalkanoate (PHA) and an additive. The twin-screw extruder (10) is not particularly limited as long as it is a known twin-screw extruder capable of mixing and melting a polymer resin. Specifically, the twin-screw extruder (10) can be a co-rotating intermeshing twin-screw extruder, a counter-rotating intermeshing twin-screw extruder, or a tangential counter-rotating twin-screw extruder.

[0096] As described above, the twin-screw extruder (10) can operate under conditions of relatively low temperature and low pressure (with controlled barrel temperature and screw rotation speed). As a result, the stress applied to the polyhydroxyalkanoate contained in the raw material is minimized; thus, a reduction in the molecular weight of the polyhydroxyalkanoate can be controlled.

[0097] Gear pump (20)

[0098] The gear pump (20) equipped in the apparatus for preparing particles according to the present disclosure is disposed at the rear end of the twin-screw extruder (10) to convey the polyhydroxyalkanoate melt. Specifically, the gear pump (20) supplies the polyhydroxyalkanoate melt formed and discharged from the twin-screw extruder (10) to the die (30). Since the gear pump (20) is disposed at the rear end of the twin-screw extruder (10), the present disclosure can smoothly convey the polyhydroxyalkanoate melt even if it has a high viscosity.

[0099] The gear pump (20) is not particularly limited as long as it is a known gear pump capable of conveying a polymer resin melt.

[0100] Die (30)

[0101] The die (30) equipped in the apparatus for preparing particles according to the present disclosure forms a polyhydroxyalkanoate melt line from the polyhydroxyalkanoate melt conveyed by the gear pump (20).

[0102] The die (30) is not particularly limited as long as it is a known die having a structure capable of extruding a polymer resin melt into a melt line having a predetermined diameter.

[0103] Underwater pelletizer (40)

[0104] The underwater pelletizer (40) equipped in the apparatus for preparing particles according to the present disclosure cuts and crystallizes the polyhydroxyalkanoate melt line formed by the die (30) to form pellets.

[0105] The underwater pelletizer (40) may include a cutting tool for cutting the polyhydroxyalkanoate melt line and a circulating water bath for cooling and crystallizing the polyhydroxyalkanoate sheet cut by the cutting tool.

[0106] The underwater pelletizer (40) is not particularly limited as long as it is a known underwater pelletizer including a cutting tool and a circulating water bath.

[0107] Modes of the present invention

[0108] Hereinafter, the present disclosure will be described in detail with reference to embodiments. However, the scope of the present disclosure is not limited to the following embodiments.

[0109] [Example 1] Preparation of pellets

[0110] 100 parts by weight of polyhydroxyalkanoate (CJ CheilJedang; 4-HB repeating unit ratio: 8 - 12 wt%) and 0.5 phr (unit of the amount of additive added per 100 parts by weight of polymer per 100 parts by weight of resin) of an additive (magnesium stearate) were mixed and fed into the hopper of a twin-screw extruder (L / D 24, 30 mm). Subsequently, the twin-screw extruder was operated at a barrel temperature of 120 to 160 °C and a screw rotation speed of 70 to 100 rpm to form a polyhydroxyalkanoate melt. Subsequently, the polyhydroxyalkanoate melt thus formed was supplied to a die through a gear pump, and the supplied polyhydroxyalkanoate melt was passed through the holes in the die at a temperature of 120 to 190 °C to form polyhydroxyalkanoate melt strands. Subsequently, the polyhydroxyalkanoate melt strands thus formed were supplied to an underwater pelletizer, cut, and then passed through a circulating water bath at 40 to 80 °C to allow crystallization. Thereafter, the particles (polyhydroxyalkanoate pellets) thus obtained were dried at a temperature of 40 °C or higher to produce particles containing polyhydroxyalkanoate.

[0111] [Comparative Example 1] Preparation of Particles

[0112] Particles containing polyhydroxyalkanoate were prepared by the same procedure as in Example 1, except that the polyhydroxyalkanoate melt was formed without adding an additive (magnesium stearate) and was directly fed to the die without a gear pump.

[0113] [Comparative Example 2] Preparation of Particles

[0114] Particles containing polyhydroxyalkanoate were prepared by the same procedure as in Example 1, except that the polyhydroxyalkanoate melt was directly fed to the die without a gear pump.

[0115] [Comparative Example 3] Preparation of Particles

[0116] Particles containing polyhydroxyalkanoate were prepared by the same procedure as in Example 1, except that the polyhydroxyalkanoate melt was formed without adding an additive (magnesium stearate).

[0117] [Test Example 1] Analysis of Weight-Average Molecular Weight and Determination of Molecular Weight Reduction Rate

[0118] In each of Example 1 and Comparative Examples 1 to 3, the weight-average molecular weight of the polyhydroxyalkanoate (PHA before extrusion) fed into the twin-screw extruder and the weight-average molecular weight of the polyhydroxyalkanoate (PHA after extrusion) contained in the particles were analyzed using gel permeation chromatography (GPC). The results are shown in Table 1 below. In the above GPC analysis, a refractive index detector (RID) was used, which used chloroform as the mobile phase and polystyrene (PS) as the standard substance.

[0119] In addition, the reduction rate (M d ) of the molecular weight is calculated according to the following Equation 1.

[0120] [Equation 1]

[0121] M d = {(M1 - M2) / M1} × 100

[0122] In Equation 1, M1 is the weight-average molecular weight of the polyhydroxyalkanoate (PHA before extrusion) contained in the raw material, and M2 is the weight-average molecular weight of the polyhydroxyalkanoate (PHA after extrusion) contained in the pellets.

[0123] [Table 1]

[0124]

[0125]

[0126] Referring to Table 1 above, in Example 1 according to the present disclosure, it was confirmed that due to the use of the additive and the gear pump, the molecular weight of PHA hardly changed, and the reduction rate of the molecular weight was 0.29%. From the above, it can be understood that when a gear pump is used, when PHA passes through the screw part of the twin-screw extruder, PHA is processed in a low-temperature and low-pressure environment, and the processed PHA is transported by the gear pump, so that PHA is directly exposed to a high-pressure environment only immediately before pelletization; therefore, the reduction of the molecular weight of PHA during pelletization can be controlled. In addition, the use of an additive can also control the reduction of the molecular weight of PHA.

[0127] Meanwhile, in Comparative Example 1 where neither the additive nor the gear pump was used, the molecular weight decreased significantly, and the reduction rate of the molecular weight was 55.63%. In Comparative Examples 2 and 3 where the additive was used or the gear pump was adopted, it was confirmed that the molecular weight changed significantly, and the reduction rates of the molecular weights of both PHAs exceeded 15%.

[0128] [Explanation of Reference Numerals]

[0129] 10: Twin-screw extruder

[0130] 20: Gear pump

[0131] 30: Die

[0132] 40: Underwater pelletizer

Claims

1. A method for preparing particles, the method comprising: (1) feeding a raw material comprising polyhydroxyalkanoate (PHA) and an additive to a twin-screw extruder to form a polyhydroxyalkanoate melt; (2) supplying the polyhydroxyalkanoate melt to the template via a gear pump; (3) passing the polyhydroxyalkanoate melt through a template to form a polyhydroxyalkanoate melt line; and (4) Cutting and crystallizing the polyhydroxyalkanoate melt strands in an underwater pelletizer to form pellets.

2. The method for preparing particles according to claim 1, wherein, In step (1), the barrel temperature of the twin-screw extruder is 120 to 160°C.

3. The method for preparing the particles according to claim 1, wherein, In step (1), the temperature of the polyhydroxyalkanoate melt is 130 to 160°C.

4. The method for preparing particles according to claim 1, wherein, In step (1), the additive includes at least one of a slip agent and a nucleating agent. 5 . The method for preparing particles according to claim 4 , wherein the amount of the additive is 0.1 to 20 parts by weight relative to 100 parts by weight of the polyhydroxyalkanoate.

6. The method for preparing particles according to claim 1, wherein, In step (1), the polyhydroxyalkanoate is a crystalline polyhydroxyalkanoate, a semicrystalline polyhydroxyalkanoate or an amorphous polyhydroxyalkanoate.

7. The method for preparing particles according to claim 1, wherein, In step (1), the polyhydroxyalkanoate is a copolymer comprising repeating units derived from at least one selected from the group consisting of 3-hydroxybutyrate (3-HB), 3-hydroxypropionate (3-HP), 3-hydroxyvalerate (3-HV), 3-hydroxyhexanoate (3-HH), 4-hydroxybutyrate (4-HB), 4-hydroxyvalerate (4-HV), 4-hydroxyhexanoate (4-HH), 5-hydroxyvalerate (5-HV) and 6-hydroxyhexanoate (6-HH).

8. The method for preparing particles according to claim 7, wherein the polyhydroxyalkanoate is a copolymer comprising repeating units derived from 4-hydroxybutyrate (4-HB), and the amount of the repeating units derived from 4-hydroxybutyrate (4-HB) is 1 to 60 wt % based on the total weight of the copolymer.

9. The method for preparing particles according to claim 7, wherein the polyhydroxyalkanoate is poly(3-hydroxybutyrate-co-4-hydroxybutyrate).

10. The method for preparing particles according to claim 1, wherein, In step (2), the differential pressure of the gear pump before and after the polyhydroxyalkanoate melt passes through is 60 to 180 bar.

11. The method for preparing particles according to claim 1, wherein, In step (3), the temperature of the template is 120 to 190°C.

12. The method for preparing particles according to claim 1, wherein, In step (4), the temperature of the circulating water bath provided in the underwater pelletizer is 40 to 80°C.

13. The method for preparing particles according to claim 1, further comprising (5) dehydrating and drying the particles formed in step (4).

14. The method for preparing the particles according to claim 1, wherein the reduction rate (M d ) of the molecular weight of the polyhydroxyalkanoate according to the following Equation 1 is 15% or less: [Equation 1] M d = {(M1 - M2) / M1} × 100 In Equation 1, M1 is the weight average molecular weight of the polyhydroxyalkanoate contained in the raw material, and M2 is the weight average molecular weight of the polyhydroxyalkanoate contained in the particles.

15. A particle produced by the production method according to any one of claims 1 to 14.

16. An apparatus for preparing particles, the apparatus comprising: a twin-screw extruder for forming a polyhydroxyalkanoate melt from a feedstock comprising a polyhydroxyalkanoate (PHA) and an additive; A gear pump, which is arranged at the rear end of the twin-screw extruder and is used to convey the polyhydroxyalkanoate melt; A die for forming a polyhydroxyalkanoate melt strand from a polyhydroxyalkanoate melt delivered by a gear pump; and An underwater pelletizer for cutting and crystallizing the polyhydroxyalkanoate melt strand formed by the die to form pellets.

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